In fact, when I used this method to do the verification of what should be cloned, I don't even know that it was possible to have no roots :( TFS is always surprising (not in a good way...)! 
Given that this method is used during a normal clone even without the the option `--with-branches` (like in #348), we can't throw an exception because we surely block some scenario we didn't think about (like the one reported).

I hope @prasanna will give us more information how he could have this case (something to clone but TFS2010 sayin that there isn't a root branch). I think that's a project migrated from a previous version and kept as a folder project and not converted to a branch.

But for the moment, it should be the better solution to solve the crash...